diyAudio - rjm
Go Back   Home > Forums > Blogs

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Old

Current Feedback Amplifier

Posted 31st January 2012 at 05:15 AM by rjm
Updated 31st January 2012 at 05:22 AM by rjm

Found this today: DC Coupled Amplifiers for Audio from an 11 year old web page by one Knut Harald Nygaard.

I've taken some minor liberties with the circuit, shown in the second, color image below. Replaced the current sources with resistors and moved the output buffer out of the feedback loop.

Note the resultant double symmetry of the dual-diamond buffer topology, highlighted in blue.
Attached Thumbnails
Click image for larger version

Name:	dcff15 original.png
Views:	1463
Size:	7.6 KB
ID:	581   Click image for larger version

Name:	dcff15 rm mod color.png
Views:	1842
Size:	14.6 KB
ID:	582  
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 2383 Comments 2 rjm is offline
Old

Whither Next for RJM Audio?

Posted 26th January 2012 at 12:22 AM by rjm
Updated 1st February 2012 at 08:20 AM by rjm

On the occasion of selling the 100th and last VSPS Stereo Kit, it's time to consider what direction(s) RJM Audio will take over the next little while.

A. A minor revision of the stereo VSPS board is planned. Just a point release to address feedback I received over the last couple of years. Point release on current boards (Phonoclone 3, VSPS 300, Sapphire) expected when I deplete existing stock and have to re-order.

B. Since my circuit designs are essentially modular (the voltage regulation of the Sapphire headphone amp could be used with the Phonoclone, the output stage of the Sapphire could be detached and used on the output buffer on the VSPS...) I'm going to work on bringing that vision to a concrete reality by developing "swap-in swap-out" circuit boards... like those toys where you can change out the head, body and legs of a character to make many variations.
  1. X-reg board
  2. Zener reg board
  3. basic op amp gain block board
  4. VSPS and
...
rjm's Avatar
rjm
diyAudio Member
Posted in Uncategorized
Views 1147 Comments 4 rjm is offline
Old

My system (Jan 2012)

Posted 23rd January 2012 at 12:12 PM by rjm
Updated 26th January 2012 at 02:57 AM by rjm

Biggest changeover in many years.

Denon DP-2000, DA-307, DL-103 turntable/tonearm/cartridge
Phonoclone 3 with 160 VA Plitron power supply
47 Labs "Treasure" model 0247 preamplifier
47 Labs "Treasure" model 0347 amplifier
Onkyo D-605SR speakers
Cables by oyaide, mostly.
(photo: Pentax K10D, Pentax FA 31mm F1.8 AL Limited)
Attached Thumbnails
Click image for larger version

Name:	IMGP1552j 1280.jpg
Views:	1101
Size:	369.4 KB
ID:	580  
rjm's Avatar
rjm
diyAudio Member
Views 1114 Comments 0 rjm is offline
Old

Oh, MY!

Posted 23rd January 2012 at 06:51 AM by rjm

Denon DL-A100

Transparent DL-103 for Denon's 100th anniversary.
Attached Thumbnails
Click image for larger version

Name:	dla100_2.jpg
Views:	199
Size:	10.3 KB
ID:	577  
rjm's Avatar
rjm
diyAudio Member
Views 803 Comments 2 rjm is offline
Old

op amps for audio

Posted 23rd January 2012 at 06:36 AM by rjm

Douglas Self on op amps for audio, which I read before in slightly different form, on another web site somewhere, many years ago... today was a refresher course.

Excerpts from op amps in small signal audio design, by D. Self [Part 1, part 2, part 3, part 4].

I suppose I should get with the times and start using the LM4562 seeing as it is available in DIP8 now. (I had this memory that it was only SOIC, go figure...) Pity it's dual only. On the other hand, that leads to some neat ideas, like a compact version of the Sapphire amp for example, or the X-reg.

I am struck by how few choices we really have when it comes to practical op amps for audio in single DIP8 packages. There is the NE5534, TL071 and TL051, the OPA134, the OPA604, and OPA27, OPA627. Maybe the AD797 but I have yet to see the point. Given that the TL1071 and derivatives are outdated and replaced essentially by the OPA134, and given the excessive cost (and questionable sonic benefit)...
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 1261 Comments 2 rjm is offline
Old

The new system, up and running.

Posted 22nd January 2012 at 10:52 AM by rjm
Updated 25th January 2012 at 07:57 AM by rjm

So now we have the model 0247 DAC/preamp/headphone amplifier and model 0347 power amplifier in the main system. That's the old Denon DP-2000 TT, Phonoclone 3, and Onkyo D-605SR speakers.

The gain of the 0347 is 30 dB, so with the 0247 doing duty as a preamp the overall gain is a tad high, but it's perfectly useable. I'll look at the passive preamp options (including the model 0447) at a later date.

Anyhow, the big news is it completely destroys the non-inverting LM3875 Gainclone I have been using for the last decade, so badly, in fact, I'm starting to wonder if my Gainclone was busted. In comparison with the 0347 it sounds like a distorted, uncontrolled mess.

Since my speakers are really very modest in quality (though at 82dB and 6 ohms, a bit of a rough load) I wasn't expecting much difference one way the other, so this comes as a severe shock.

Unfortunately I'm not within reach of a good reference system to give the 0347 a real evaluation....
Attached Thumbnails
Click image for larger version

Name:	IMGP1513j 1280.jpg
Views:	717
Size:	348.1 KB
ID:	576  
rjm's Avatar
rjm
diyAudio Member
Views 1099 Comments 1 rjm is offline
Old

47 Labs Treasure 0347 : trials and tribulations

Posted 20th January 2012 at 11:48 AM by rjm

And not even sure what a tribulation is, but I'm sure I've had at least one building this amp.

Like the 0247 it's not so much difficult as it is painstaking hard work. The output transistors have to be mounted "just so" so the boards screw to the case properly, the wiring of the thermal protection transistors and gluing them to the output devices is tricky and easy to mess up.

I triple-checked and was rewarded by, it seems, error free boards. I messed up and wired the mute switch incorrectly though (the photos show it wrong, in case you come across this blog post looking for help) and I think the switch has a fault somehow as L and R channels appear to me mixed together. Taming the offsets gave me considerable grief but I think its all OK now.

Tomorrow I'll hook it up to the speakers and see what happens.
Attached Thumbnails
Click image for larger version

Name:	DSC_3005 1280.jpg
Views:	1517
Size:	311.5 KB
ID:	569   Click image for larger version

Name:	DSC_2991 1280.jpg
Views:	1881
Size:	401.7 KB
ID:	570   Click image for larger version

Name:	DSC_2969 1280.jpg
Views:	1140
Size:	243.7 KB
ID:	571   Click image for larger version

Name:	DSC_3007 1280.jpg
Views:	2170
Size:	290.9 KB
ID:	572  
rjm's Avatar
rjm
diyAudio Member
Views 2012 Comments 1 rjm is offline
Old

A different design aesthetic.

Posted 17th January 2012 at 10:52 AM by rjm
Updated 25th January 2012 at 10:21 PM by rjm

I like the concept of appearance in high-end audio. I mean, where the look of the equipment makes a statement about what it's all about inside.

The 0347 is proportioned like a vintage tube receiver, but in miniature. It even has the lit, transparent front panel where the radio tuning strip would have resided. The heavy grey hammertone and very simple, basic hardware are reminiscent of Heathkit or Dynaco. In short, the appearance evokes the spirit of a simpler, more innocent age of vintage hifi without being a slavish replica.
Attached Thumbnails
Click image for larger version

Name:	DSC_2962 1280.jpg
Views:	587
Size:	276.3 KB
ID:	568  
rjm's Avatar
rjm
diyAudio Member
Views 840 Comments 0 rjm is offline
Old

Another package in the mail...

Posted 14th January 2012 at 10:30 AM by rjm

The 47 Labs "Treasure" stereo amplifier kit model 0367 has just arrived here at RJM Audio central command.

61,500 yen delivered, a tad more than the model 0247 headphone amplifier / DAC. Basically lose the volume control and DAC board, gain a bigger transformer and a thick aluminum bottom plate that serves as the heatsink... the amplifier circuit itself is almost identical, just with a slightly bulked-up output stage and the addition of certain safety considerations such as fine tune-able bias current and thermal protection for the output transistors.

Which makes an unusual circuit for a power amplifier: the output stage is a unity gain current buffer running open loop. For a headphone amp that's justafiable because the bias current is such that the amp will almost always be running in class A. For a power amp rated 40 W into 4 ohms, it's class AB.

Mr. Tsukahara seems pretty pleased with the result though, and I am anxious to try it...
Attached Thumbnails
Click image for larger version

Name:	DSC_1012 1280.jpg
Views:	594
Size:	360.8 KB
ID:	567  
rjm's Avatar
rjm
diyAudio Member
Views 723 Comments 0 rjm is offline
Old

This vs. that.

Posted 12th January 2012 at 11:41 PM by rjm
Updated 26th January 2012 at 05:42 AM by rjm

47 Labs 0247 vs. RJM Audio Sapphire

I wasn't even aware that the folks at 47 Labs were developing a headphone amplifier until after the Sapphire was finished, and I'm sure they didn't know what I was working on, so it's all the more remarkable just how similar the two designs are. Two separate answers from two separate people sharing the same general design philosophy.

Similarities:

- Solid state op amp voltage stage front end and solid state push-pull buffer running open loop for the output stage.
- Gain of 5-6x (14-16 dB)
- 20-30 mA bias current in the output stage.
- All BJT circuit** (see footnote)
- Use of "diamond buffer" circuit element. (Albeit in very different ways)
- 10 V voltage rails, split supply.

Differences:

- My voltage stage is an OPA134, or any 8 pin DIP op amp IC. 47 Labs voltage stage is a fully discrete current feedback op amp with a diamond buffer...
rjm's Avatar
rjm
diyAudio Member
Views 812 Comments 1 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 08:24 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2